This invention relates to biosorption processes for removal and recovery of heavy metals, radionuclides, pollutants and other materials from the environment.
The existence of heavy metals and radionuclides and pollutants such as dye stuffs in the environment represent a long-term environmental hazard (Gadd and White [1993] Trends in Biotechnol., 11, 353). In many cases, when these materials are introduced into the environment they are taken up by biological systems including plant and microbial materials. It has been proposed that this phenomenon, known as biosorption, might be exploited in biotechnological processes relating to metal removal/recovery from mining wastes, domestic and industrial wastes and removal of radionuclide contaminants present in waste waters from the nuclear industry (McHale and McHale, [1994] Biotechnol. Advances, 12, 647).
Although biosorption results in the uptake of metals and radionuclides by microorganisms, no single mechanism responsible for uptake has been identified. The term xe2x80x9cadsorptionxe2x80x9d suggests binding of a material to the surface of an adsorbent. The term xe2x80x9cabsorptionxe2x80x9d implies penetration of the sorbate through the surface to an inner matrix. Since the uptake of metals/radionuclides and other agents by microbes appears to involve both types of process, the term xe2x80x9cbiosorptionxe2x80x9d is most commonly applied to describe the phenomenon.
In any previously proposed bioremediation systems concerned with exploiting biosorptive processes, one of the major problems encountered has been the efficient separation of the biosorbent material from the relevant waste water stream, particularly if large volumes are to be processed. In many cases workers in the field have suggested the use of immobilization systems in order to facilitate re-use of the biosorbent material. It has also been proposed that this would also facilitate efficient separation from the relevant waste-water stream and aid in the regeneration of the biosorbent (McHale and McHale [1994] (Biotechnol Advances), 12, 647).
In addition to the above complications associated with the exploitation of biosorptive processes, solutions of metals/radionuclides and other pollutants in waste-water streams tend to be very dilute. Since biosorptive processes, particularly using non-living biomass are in many cases equilibrium events, the inventors have found that uptake of the relevant sorbate is usually enhanced by positively disturbing those equilibria. They postulate that increasing the concentration of the sorbate in the vicinity of the biosorbent may tend to increase the degree of uptake exhibited by any form of biomass.
Distribution of ions across a semipermeable membrane is also an equilibrium event. However, removal of free or soluble ions from solution within a membrane enclosed compartment tends to unbalance that equilibrium and the net flow of ions into the membrane enclosed space. The inventors suggest that placing biosorbent material inside a membrane-enclosed compartment and exposing this to an external solution of ions would result in a net flow of those ions into the enclosed space. In effect this would achieve ion removal from the external solution by a mechanism known as non-equilibrium dialysis. It has the added advantage of ensuring biosorbent and sorbate separation before, during and after the ion removal/recovery process.
Although this offers many advantages over conventional biosorption processes, this type of system would be highly dependant on the rate of diffusion into the inner compartment. It has previously been shown however that it is possible to attract ions into membrane-enclosed compartments using an electric field and this is referred to a electrodialysis (Bobrinskaya et al., [1995] Russian J. Applied Chem. 68, 1205; Ishimaru [1994] Desalination, 98, 485.). It has been suggested that this may be exploited in processes such as desalination of water although it is worth noting that removal of the applied electric field in conventional electrodialysis modalities, results in leakage of the relevant ions from the membrane-enclosed space.
It is one object of the present invention to provide a system to remove and/or recover heavy metals/metals/ionic species/radionuclides and/or pollutants in general from the environment.
According to the present invention there is provided a system for separating biosorbent and sorbate, the system comprising biomass enclosed within a membrane system coupled to an electrode capable of being placed in contact with sorbate containing material in the presence of a counter electrode such that an electric field may be discharged across the electrodes and ionic species will migrate into the membrane enclosed system.
Accordingly in one aspect the invention provides a biosorption process comprising exposing sorbate containing material to biomass enclosed within a membrane system and generating an electric field across the membrane thereby causing sorbate to migrate to the biomass.
In another aspect the invention provides biosorption apparatus comprising biomass enclosed within a membrane system coupled to or capable of being coupled to an electrode.
In another aspect the invention relates to the use of immobilised biomass in a system, apparatus or process as described herein.
The biomass material may be living or non-living, modified or non-modified, free or immobilised or any combination of these forms.
In a particular embodiment the biomass is distillery biomass.
In the system the migrated species within the membrane can be taken up and processed by the biosorptive processes of the biomass.
The electric field in the system may be generated in a conventional manner and/or from renewable energy sources including solar, wind and wave energy forms.
Suitably the system may be used to remove metals/heavy metals/radionuclides and/or other pollutants from natural and artificial sources and/or combinations thereof.
In one embodiment the invention provides an apparatus comprising modified non-living biomass enclosed within a membrane system coupled to a platinum electrode.
Alternatively the biomass may be non-living.
The electrode may be of any other electrode material.
The apparatus may be placed in contact with the sorbate-containing material in the present of a counter electrode. An electric field will be discharged across the electrodes and the ionic species will migrate into the membrane enclosed system. The migrated species within the membrane enclosed space will then be taken up by the biosorptive processes exhibited by the biomass.
The living or non-living biomass may be modified.
The living or non-living biomass may be immobilised.
In the embodiment described above the electric filed may be generated in the conventional manner and/or from renewable energy resources including, although not exclusively, solar, wind and wave energy forms.
In another embodiment the invention provides a device (or derivative thereof) based on the use of electrodiffusion-assisted biosorption and capable of removing metals/heavy metals/radionuclides/and/or other pollutants from natural and artificial sources and/or combinations thereof) for the purposes of bioremediation and/or substance recovery.
The device (or derivative thereof) based on the use of electrodiffusion-assisted biosorption may be capable of concentrating agents for analytical purposes.
In a third embodiment the invention provides a system capable of generation of ionic species and subsequent sequestration of these by the systems described herein.
The embodiments of the invention may be operated in batch, fed-batch and/or continuous modes including combinations thereof.
The embodiments of the invention may be operated in conjunction with other processes.
The invention will comprise any of the above systems and/or combinations of the above.